Efficient, Stable, and Solvent-Free Synthesized Single-Atom Catalysts: Carbonized Transition Metal-Doped ZIF-8 for the Hydrogen Evolution Reaction**

Abstract

Herein we present non-noble metal single-atom catalysts (SACs) based on carbonized transition metal-doped zeolitic imidazolate frameworks (ZIFs) as stable and efficient electrocatalysts for the hydrogen evolution reaction in acidic media. In this work, earth-abundant metals are embedded in a porous N-rich carbon matrix by pyrolyzing metal-doped ZIF structures and characterized by spectroscopic, microscopic, and electrochemical methods. The complete synthesis of these high surface area SACs was carried out without any solvents and hence offers a promising route for a more sustainable catalyst production and industrial upscaling. As the best-performing catalyst, cobalt SAC illustrated already with a low cobalt loading of <0.3 at.% a substantial increase in activity with an overpotential of −322 mV for −10 mA cm−2, and high stability during electrolysis at −10 mA cm−2 for 12 h in acidic media, with only a small decrease of 33 mV to more negative potentials after the initiation period.